Adamantane is known as a highly symmetrical cage compound which has a chemical constitution same as the constitution unit of diamond. Adamantane as a chemical substance is characterized by its (1) low energy of molecular strain and excellent heat resistance, (2) high dissolvability of fat and oil due to high carbon density, (3) less odor in spite of its sublimation properties and the like. Accordingly, attention has been paid since 1980 age to its availability in pharmaceutical field for raw materials of therapeutic drug for parkinsonism and therapeutic drug for influenza. Moreover in recent years, the characteristics such as heat resistance and transparency that are imparted to adamantane derivatives have attracted special attention in the fields of optical material such as photoresist for semiconductor production, magnetic recording medium, optical fiber, optical lens and optical disc substrate material; functional materials such as heat resistant plastics, coating material and adhesive; cosmetics; lubricating oil and the like, thereby expanding the application of the adamantane derivatives. In addition, the demands thereof have increased in the field of pharmaceuticals such as raw materials for anticancer drug, cerebral function-improving agent, therapeutic drug for neurological disorder and antiviral drug.
The technology of converting a hydrocarbon compound into an alcohol and a ketone through oxidation is technology of extreme industrial importance from the viewpoint of effective utilization of carbon resources. Although there has been industrially applied technology of producing an alcohol and a ketone from a monocyclic aliphatic compound such as cyclohexane, there has not yet been developed any technology of selectively efficiently producing a monohydric alcohol and a ketone through selective oxidation of a polycyclic aliphatic compound bearing secondary or tertiary carbon atoms.
In recent years, 2-adamantanol and 2-adamantanone from among adamantane derivatives have come to be spotlighted each as an important intermediate of a variety of pharmaceuticals and functional materials. However in the case of producing an alcohol by reacting adamantane with an oxidizing agent, the tertiary carbon atoms present in four numbers in one molecule thereof predominantly react to form not only a monohydric alcohol but also a dihydric alcohol and a trihydric alcohol, thereby making it impossible to selectively produce 2-adamantanol. In addition, 2-adamantanone is produced only by a process in which adamantane is heated and reacted in concentrated sulfuric acid.
As technology of producing adamantanol by oxidizing adamantane, there is known the technology in which adamantane is oxidized with oxygen in the presence of an imide compound (such as N-hydroxyphthalimide or the like) as a catalyst and a transition metal complex as a promoter {refer to Japanese Patent Application Laid-Open No. 327626/1997 (Heisei 9)}. Nevertheless, this technology suffers from low selectivity to a monohydric alcohol.
Further as technology of producing an oxocompound derivative (such as ketone), there is disclosed the catalytic technology in which a strong acid is added to the above-mentioned phthalimide compound as a catalyst and a transition metal complex as a promoter {refer to Japanese Patent Application Laid-Open No. 309469/1998 (Heisei 10)}. However, this technology suffers from low selectivity to the objective product and besides the formation of unfavorable byproducts such as 1-hydroxyadamantanone, 1-adamantanone, 1,3-adamantanediol and adamantanediol.
On the other hand, as technology other than the use of the above-mentioned phthalimide based catalyst, there is known a process for producing an alcohol and a ketone which comprises reacting adamantane in the presence of a transition metal complex having a porphyrin based organic compound as a ligand and of an aldehyde analogue {refer to Japanese Patent Application Laid-Open No. 87216/1997 (Heisei 9)}. Nevertheless, this process involves such problems as extremely low yield of adamantanol as low as 4.6% and 2-adamantanone as low as 0.7%, low selectivity to the objective products and besides the necessity for the coexistence of an expensive aldehyde analogue as a reducing agent.
In addition, there is reported a process for producing adamantanol which comprises hydroxylating an adamantane analogue in the presence of a ruthenium compound and hypochlorous acid or a salt thereof (refer to Japanese Patent Application Laid-Open No. 219646/2000). However, it is impossible for this process to selectively produce the objective 2-adamantanol, since the principal alcohol products are 1-adamantanol and 1,3-diadamantanol.
As technology for selectively producing 2-adamantanol, there is publicly well known a process for experimentally producing the same in concentrated sulfuric acid. For instance, it is reported by Schlatmann that 2-adamantanol is obtained at a yield of 72% by maintaining 1-adamantanol under heating at 30° C. for 12 hours in concentrated sulfuric acid {refer to Tetrahadronn: 24, 5361 (1968)}. There is proposed a process in which the reaction is put into practice under a two stage temperature condition as improved technology for the above-mentioned process wherein highly oxidative concentrated sulfuric acid is used also as a solvent {refer to Japanese Patent Application Laid-Open No. 189564/1999 (Heisei 11)}. Although this process enhances the yield of adamantanone, the problems still remain unsolved in that a large amount of concentrated sulfuric acid is used, thereby complicating the step of separation and refining after the reaction and at a the same time, necessitating the use of expensive and corrosion-resistant equipment and a material.